Problem: Perform the row operation, $R_1 \leftrightarrow R_2$, on the following matrix. $\left[\begin{array} {ccc} 3 & 0 & 0 & -1 \\ -3 & 2 & -6 & 1 \\ 4 & 2 & 7 & 9 \end{array} \right] $
Background There are three basic row operations that can be performed on matrices. $R_i \leftrightarrow R_j$. This symbol tells us to interchange rows $i$ and $j$. $cR_i \rightarrow R_i$. This symbol tells us to multiply a row $i$ by a constant $c$. $R_i + cR_j \rightarrow R_i$. This symbol tells us to add $c$ times row $j$ to row $i$. Switching the rows For the given matrix, $R_1$ and $R_2$ are given below. $R_1=\left[\begin{array} {ccc} 3 & 0 & 0 & -1 \end{array} \right] ~~~~~ R_2=\left[\begin{array} {ccc} -3 & 2 & -6 & 1 \end{array} \right]$ $\left[\begin{array} {ccc} 3 & 0 & 0 & -1 \\ -3 & 2 & -6 & 1 \\ 4 & 2 & 7 & 9 \end{array} \right] \xrightarrow{R_1 \leftrightarrow R_2}\left[\begin{array} {ccc} -3 & 2 & -6 & 1 \\ 3 & 0 & 0 & -1 \\ 4 & 2 & 7 & 9 \end{array} \right] $ Summary Our resultant matrix is the following. $\left[\begin{array} {ccc} -3 & 2 & -6 & 1 \\ 3 & 0 & 0 & -1 \\ 4 & 2 & 7 & 9 \end{array} \right]$